Fix UI glitches on Performance and Memory panels

third_party/WebKit/Source/devtools/front_end/timeline/TimelineNetworkFlameChart.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @implements {PerfUI.FlameChartDataProvider}
  * @unrestricted
  */
 Timeline.TimelineFlameChartNetworkDataProvider = class {
   /**
    * @param {!TimelineModel.TimelineModel} model
    */
   constructor(model) {
     this._font = '11px ' + Host.fontFamily();
     this._model = model;
     this.reset();
     this._style = {
       padding: 4,
       height: 17,
       collapsible: true,
       color: UI.themeSupport.patchColor('#222', UI.ThemeSupport.ColorUsage.Foreground),
       font: this._font,
       backgroundColor: UI.themeSupport.patchColor('white', UI.ThemeSupport.ColorUsage.Background),
       nestingLevel: 0,
       useFirstLineForOverview: false,
       useDecoratorsForOverview: true,
       shareHeaderLine: false
     };
-    this._group = {startLevel: 0, name: Common.UIString('Network'), expanded: true, style: this._style};
+    this._group = {startLevel: 0, name: Common.UIString('Network'), expanded: false, style: this._style};
   }
 
   /**
    * @return {boolean}
    */
   isEmpty() {
     this.timelineData();
     return this._maxLevel === 0;
   }
 
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   /**
    * @override
    * @param {number} entryIndex
    * @return {boolean}
    */
   canJumpToEntry(entryIndex) {
     return false;
   }
 };